I put a new Centos6 haproxy (compiled) system in production with 700+ sites behind it. The load was not high on the proxy or the two backend IIS servers. We were noticing occasional 503 errors on a handful of sites. While getting 503 at the client the site worked directly on the IIS servers. Also I could use curl and wget successfully from haproxy during the issues. After an hour the breif outages were not dissipating and we reverted to our previous load balancer.

Has anyone seen an issue like this that was caused by configuration error or that there is something I can look for?